SONET GLOSSARY

Last Updated November 28, 1998

This glossary is a work in progress and will be updated from time to time.
The glossary is meant to be more than just a list of acronyms but I try to
give enough explanation of each term so that it adds to the readers understanding
of SONET in general. The source for this material comes mostly from Bellcore,
ANSI standards, and publications. It has been aggregated and condensed
here in a glossary format. If you find an error or have items that
you feel should be added to the list please Email:
webmaster@sonet.com

A

ADM - add-drop-multiplexer. This is one of SONET's claim to fame.
The tributaries of a SONET transport stream, are synchronously multiplexed
to the line rate, i.e. there are no stuff bits or stuff opportunity bits
as is the case in the plesiochronous hierarchy. As such an ADM can insert
or extract lower rate tributary data without demultiplexing the aggregate
line rate.

AIS - alarm indicator signal. This is a coded signal that is sent
to downstream network elements to indicate that an upstream failure has been
detected and alarmed.

Asynchronous Mapping - These mappings are defined for clear channel
transport of digital signals that meet the standard DSX cross connect
requirements, typically DSX-1 and DSX-3 in most practical applications. At
the asynchronous mapping interface, frame acquisition and generation is not
required. For example if your system can transport a BERT (bit error test
set) signal with a 10^23-1 test pattern, it is being asynchronously mapped
for transport. And they call this SONET?

APS - Automatic Protection Switching.

A 1+1 protection switch architecture is one in which the head end signal
is permanently bridged (at the electrical level) to service service and
protection equipment to enable the same payload to be transmitted identically
to the tail end service and protection equipment. At the tail end , each
service and protection optical signal is monitored independently and identically
for failures. The receiving equipment selects either the service or protection
channel based upon the switching criteria.

A 1:N protection switch architecture is defined as an architecture in which
any one of N service channels can be bridged to a single optical protection
channel. Head end to tail end communications are accomplished by using the
SONET APS channel, bytes K1 and K2.

Availability - The foundation for many Bellcore reliability criteria
is an end to end two way availability of objective of 99.98% for interoffice
applications (0.02% unavailability or 105 minuters/year down time). The objective
for loop transport between the central office and the customer premises is
99.99%. For interoffice transport the objective refers to a two way broadband
channel, e.g. SONET OC-N, over a 250 mile path. For loop applications the
objective refers to a two way narrowband channel, e.g. DS0 or equivalent.

B

BIP-8 - Bit interleaved parity 8, is a method used for error monitoring
where each bit of the BIP-8 code word or byte, corresponds to even parity
as calculated across matching bit positions for the distinct bytes in a SONET
frame. That is the first BIP-8 bit would correspond to even parity across
bit number 1 of a certain number of bytes in the SONET frame. The certain
number of bytes depends upon whether you are calculating section, line, or
path BIP-8.

BIP-8 vs BER

BER

Max. Detection Time

BIP-8 Violations

10e-3

10 ms

344xN

10e-4

100 ms

492xN

10-5

1s

510xN

10e-6

10s

512xN

10e-7

100s

512xN

10e-8

1000s

512xN

10e-9

10,000s

512xN

Where N is the N in OC-N

The BIP violations are counted over a sliding time window equal to the maximum
detection time. The BIP-8 violation counts of individual STS-1s of an STS-N
are added together. The above values take into account the error detection
saturation effect at high BER.

Design objectives for the for the average detection time depend on
the level N of the Optical Carrier and are typically an order of magnitude
lower than the Max. detection times shown in the above table for OC-3. As
the optical rate increases the average detection time decreases proportionally.

BITS - Building Integrated Timing Supply. A single building master
timing supply. BITS generally supplies DS1 and DS0 level timing throughout
an office. The BITS concept minimizes the number of synchronization links
entering an office, since only the BITS will receive timing from outside
the office.

Brillouin Scattering - Stimulated Brillouin scattering is an interaction
between the optical signal and the acoustic waves in the fiber that causes
the optical power to be scattered backwards towards the transmitter. It
is a narrowband process that effects each channel in a DWDM system individually.
It is noticeable in systems that have channel powers in excess of 5
- 6 dBm. In most cases SBS can be suppressed by modulating the laser
transmitter to broaden the line width.

B3ZS - Bipolar with 3 zero substitution. This is the STS-1 line code.
In the B3ZS technique each block of 3 consecutive zeros is removed and replaced
with {B0V} or {00V}. The choice is made such that the number of B pulses
between consecutive V pulses is odd. Where B represents the normal bipolar
pulse and V represents a bipolar violation.

Concatenated STS-Nc - An STS line signal in which the STS envelope
capacities from N STS-1s are transported as a single entity as opposed to
being treated as separate signals. The STS-Nc shall be multiplexed, switched,
and transported over the network as a single entity.

CMI - Coded Mark Inversion. This is the STS-3 line code. This is a
two level non-return to zero code. A binary 1 is coded by either of the amplitude
levels, +A or -A, for one full unit time interval (T) in such a way that
the level alternates for successive binary ones. For a binary zero there
is always a positive transition (-A to +A) at the mid point of the binary
unit interval (T/2).

Clock Free Run Mode - An operating condition of a clock in which its
local oscillator is not locked to an external synchronization reference,
and is using no storage techniques to sustain it's accuracy.

Clock Holdover Mode - An operating condition of a clock in which its
local oscillator is not locked to an external synchronization reference but
which is using storage techniques to maintain its accuracy with respect to
the last known frequency comparison with a synchronization reference.

Collapsed Ring - A topology where the ring resides entirely within
a single fiber bundle. In the event of a cable cut the ring is severed
in two places.

D

DCC - Data Communications Channel, in the section layer, 3 bytes
(D1,D2,D3) are allocated in STS-1 number 1 of an STS-N signal for section
data communications. These 3 bytes are treated as one 192kbs data channel
for the transmission of alarms, maintenance, control, administration as well
as other network element communication needs. In the line layer, 9 bytes
(D4-D12) are used as a 576kbs data channel for similar purposes.

Dispersion - More correctly known as chromatic dispersion.
Dispersion results when light of different wavelengths propagates at
different velocities down a fiber span. The result is pulse spreading
that is a function of length. Total dispersion is measured in units
of ps/nm and the dispersion coefficient of a fiber is in units of
ps/nm-km, or pico-seconds per nanometer per km of fiber length.

Drop and Broadcast - A cross connect typically used to enable a broadcast
transmission. A signal in the high speed time slot is used to
provide simultaneous drops at more than one node. A distance learning
application would use drop and continue to feed multiple classrooms.

DS4NA - The DS4NA (where NA stands for North America) is specified
for a 139.264 Mb/s interface (not 274 Mb/s as referenced in some literature
with regard to DS-4 systems. This specification is compatible with CCITT
Recommendations G.755 for multiplexing 45Mb/s signals into 139 Mb/s signals,
but does not specify the multiplexing of other signals into the 139 Mb/s
signal.

Dual Ring Internetworking - A topology where two rings are connected
at two a different nodes providing traffic an alternate path from one ring
to another.

E

F

FEBE - Far End Block Error, a signal returned to the transmitting
network element indicating that an errored block has been received at the
receiving network element.

FERF - Far End Receive Failure. A line FERF alerts the upstream network
element that a failure has been detected along the downstream line. A line
FERF is different from a yellow signal in that a yellow signal can be used
for trunk conditioning.

Four Wave Mixing - FWM is basically an intermodulation and cross talk
phenomenon that occurs in WDM systems due to the non-linear nature of the
fiber optic cable. The effect occurs in areas of zero dispersion as
the signals need to be traveling at the same velocity in the fiber for the
effect to occur. FWM does not occur in the 1550nm window unless the
fiber is dispersion shifted.

G

GNE - Gateway Network Element. A GNE internetworks two different kinds
of networks. In SONET there are three different types of GNEs:

A GNE that interworks an X.25 DCN (Data Comm. Network) and the SONET DCC.

A GNE that interworks an X.25 DCN and an intra-site LAN.

A GNE that interworks an intra-site LAN and the SONET DCC.

Another GNE network function is message concentration for the X.25 DCN. Instead
of having one X.25 virtual circuit to each SONET network element, the gateway
can provide and X.25 virtual circuit it and the OS which can be used for
messages to and from the OS and subtending network elements on the SONET
network.

H

HDB3 - High Density Bipolar 3 coding. The European equivalent of B3ZS.

I

Intermediate NE - Intermediate Network Element (INE), has one or more
subtending NEs and performs routing for tandem traffic. An INE must support
IS-IS (Intermediate System) level 1 routing and the IS role of the ES-IS
(End System) protocol. The role a given SONET NE supports (GNE, INE, ENE)
depends upon the operations communications network architecture.

Jitter - Timing jitter is the short term variation of a digital signal's
significant instant from their ideal positions in time, where short term
implies phase oscillations of frequency greater than or equal to 10Hz.
Significant instants include for instance, optimum sampling instants. Long
term variations, where the variations are of frequency less than 10Hz, are
called wander.

Jitter Generation - The process whereby jitter appears at the output
port of an individual piece of digital equipment in the absence of applied
jitter at the input. When looped back at the high speed rate, whether or
not a standard interface exists at the higher rate, Category I equipment
must produce less than 0.3 Unit Intervals (UI) of rms jitter and less than
1.0 UI of peak-to-peak timing jitter at the output of the terminal receiver.
This is as specified in TR-499. In TR-253 for SONET a DS-3 interface shall
generate jitter less than 0.4 UI peak-to-peak.

Jitter Tolerance - For STS-N electrical interfaces input jitter tolerance
is the maximum amplitude of sinusoidal jitter at a given jitter frequency,
which when modulating the signal at an equipment input port, results in no
more than two errored seconds cumulative, where these errored seconds are
integrated over successive 30 second measurement intervals. Requirements
on input jitter tolerance as just stated, are specified in terms of compliance
with a jitter mask, which represents a combination of points. Each point
corresponds to a minimum amplitude of sinusoidal jitter at a given
jitter frequency which when modulating the signal at the equipment input
port results in two or fewer errored seconds in a 30 second measurement interval.
For the OC-N optical interface it is defined as the amplitude of the peak-to-peak
sinusoidal jitter applied at the input of an OC-N interface that causes a
1 db power penalty.

Jitter Transfer - This is the relationship between jitter applied
at the input port and the jitter appearing at the output port.

K

Kerr-effect - Optical Kerr-effect is where the index of refraction
of a fiber optic varies with the intensity of the transmitted light. This
is a non-linear process that occurs when the product of the laser power and
the effective system length becomes a significant fraction of the nonlinearity
coefficient y. At 1550 nm, 1/y ranges from 700 mW-Km
for unshifted single mode fiber to 500 mW-Km for NZDSF (Non Zero Dispersion
Shifted Fiber). In systems with milliwatt transmitters and hundreds
of Km span lengths nonlinear diffraction will occur. The main effect
of this is self phase modulation of the signal

L

Line AIS - Is generated by the section terminating equipment upon
loss of an input signal, loss of frame, or equipment failure. The line AIS
maintains operation of downstream regenerators preventing generation of
unnecessary alarms.

Long Reach - LR optical interfaces refer to optical sections with
system loss budgets from 10 db up to 28 db at OC-3, to 24 db at OC-12, and
to 20 db at OC-48. Typical of long haul telecommunications systems, LR interfaces
are based on high power, e.g. 500uW or -3dbm, Multi-Longitudinal Mode (MLM)
or Single-Longitudinal Mode (SLM) lasers.

M

Mediation Device - is a device that facilitates communications between
a SONET network and an OS.

Multiplex Process - STS-N signals are formed by byte interleaving
STS-1 signals. Three STS-1 signals shall be interleaved, one byte at a time,
to form an STS-3 signal. The first byte of the STS-3 signal shall be the
A1 byte of STS-1 number 1, followed sequentially by the A1 byte from STS-1
number 2, then the A1 byte from STS-1 number 3. The first bit to be transmitted
in the STS-3 is the most significant bit of the A1 framing byte from STS-1
number 1.

N

NRZ - The optical line coding used in SONET systems. A one or zero
are designated by a constant levels of opposite polarity.

NZDSF - Non Zero Dispersion Shifted Fiber. This type of fiber
was designed to introduce a small amount of dispersion without the zero point
crossing being in the WDM passband. With this type of fiber you can
eliminate, or at least greatly reduce the degradation due to four wave mixing
, a distortion mechanism that requires the spectral components to be phase
matched along the fiber.

O

P

PMD - Polarization Mode Dispersion. Light transmitted down a
single mode fiber can be decomposed into two perpendicular polarization
components. Distortion results due to each polarization propagating
at a different velocity. PMD causes pulse spreading as the polarizations
arrive at different times. The longer the span the worse the PMD. Total
PMD = PMDc x (L)^1/2, where PMDc is the PMD coefficient and L is the length
of the fiber. PMDc has the units of ps/(Km)^1/2, that
is pico-seconds per root Km. PMD is generally not a factor at OC-48
but will be a factor at OC-192. Corning has stated that they have conducted
field measurements on various installed SMF-28 fibers and have typical installed
link centered at less than 0.1ps/(Km)^1/2. Beginning in 1994 Corning
also implemented a fiber PMD specification of <0.5ps/(Km)^1/2 for SMF-28
and Titan single mode fibers. For OC-192 this level of PMD probably
will meet most common span engineering requirements.

Pulse Density - At all digital interfaces, digital bit streams must
contain sufficient energy for self extraction of a timing signal. The level
of energy is controlled by ensuring that the signal has a sufficient number
of pulses as specified by a pulse density. In general as the bit rate increases
the desired level of pulse density also increases, resulting in different
requirements being applied to different levels in the digital hierarchy.

Q

R

Raman Scattering - Stimulated Raman scattering is the result of
interaction between the optical signal and silica molecules in the fiber.
This process is broadband and applies to the overall optical spectrum
being transmitted. SRS manifests itself as a transfer of power from
the shorter wavelengths to the longer wavelengths, i.e. from higher photon
energy wavelengths to lower photon energy longer wavelengths. This
will result in the optical spectrum having a tilt. The effect increases
with power and the width of the DWDM spectrum. One way to mitigate
the effect is to use moderate channel powers and a densely packed spectrum.

S

Short Reach - SR optical interfaces refer to optical sections having
system loss budgets from 0 db to 7 db. Depending on the SONET hierarchical
level , SR transmitters may be either LEDs or low power MLM (multi-longitudinal
Mode) lasers.

Stratum Level - Clocks used to time signals in the digital hierarchy
are divided into levels. Stratum 1 is the highest level of accuracy
and stability.

Stratum Levels

Stratum Level

Free Run Accuracy

Holdover Stability

1

+/- 1x10^-11

N/A

2

+/- 1.6x10^-8

+/- 1x10^-10 per day

3E

+/- 4.6x10^-6

+/- 1x10^-8 per day

for the first 24 hrs.

3

+/- 4.6x10^-6

+/- 3.7x10^-7 per day

for the first 24 hrs.

SONET minimum clock

+/- 20x10^-6

Under Study

T

TARP - TID Address Resolution Protocol. This is used on a NE-NE interface
when there is a need to translate the TID of TL-1 messages to the CLNP address
(NSAP, network service access point) of an NE. The protocol would typically
be used by a GNE in a TL-1/X.25 network that needs to map TIDS to NSAPs in
a subtending network.

Transmission Delay - To control echo and to minimize the effect on
digital throughput, the maximum (one way absolute delay for steady state
operation of a 100 mile transport system with no intermediate terminals is
1ms. This applies for all interface options provided. The required maximum
delay for shorter systems is to be decreased in direct proportion to the
route mileage.